1. Field of the Invention
The present invention relates to a method of driving a display device, and more particularly, to a method of driving a liquid crystal display device that improves degradation of an image quality and reduces power consumption of a backlight unit.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices produce images by applying an electric field to a liquid crystal material, which has dielectric anisotropy and is interposed between two substrates, controlling intensity of the electric field, and adjusting an amount of light transmitted thought the substrates.
An LCD device includes a liquid crystal panel having two substrates and a liquid crystal layer interposed therebetween. A plurality of gate lines are formed on one of the two substrates, and a plurality of data lines are insulated from and cross the plurality of gate lines. Pixels are defined by the gate lines and the data lines. A thin film transistor is disposed at each crossing of the gate lines and the data lines.
The LCD device further includes a backlight unit for providing light to the liquid crystal panel. Power consumption of the backlight unit is as high as the backlight unit occupies about 70 to 80 percent of a total power of a liquid crystal display device in small devices of less than 10 inches such as cellular phones.
Recently, to reduce the power consumption of the backlight unit, various methods have been proposed. Hereinafter, a method of driving a liquid crystal display device according to a first embodiment of the related art, which may be referred to as “frame maximum data method,” will be described with reference to FIG. 1. is a flow chart of illustrating a method of driving an LCD device according to a first embodiment of the related art.
At step st1, source image data Ds corresponding to one frame, each of which has one of m gray level values (m is a natural number), are inputted as n bit digital data (n is a natural number) from exterior circuits such as a timing controller. Here, m is 2n, and the inputted source image data Ds are R, G, and B color image data that are supplied to a liquid crystal panel to produce an image. For example, in a QVGA (Quarter Video Graphics Array) model having 320×240 pixels, each of which includes three sub-pixels, the number of the source image data Ds is 76,800×3.
At step st2, a maximum image data Dmax is determined by detecting one having the largest gray level value from the source image data Ds.
Next, at step st3, the maximum image data Dmax is data-modulated such that the maximum image data Dmax has the maximum gray level value, that is, the mth gray level value, and thus a modulation factor s is calculated. The modulation factor s has the same meaning as a gain.
At step st4, conversion image data Dc are generated by data-modulating each of the source image data Ds s times. For example, in the QVGA model, each of 76,800×3 source image data is data-modulated by s times.
Through the steps st1 to st4, the source image data Ds are converted to the conversion image data Dc having increased gray level values.
At step st5, the conversion image data Dc are inputted into the liquid crystal panel to display an image. Accordingly, the image displayed on the liquid crystal panel by the conversion image data Dc has a higher brightness than an image by the source image data Ds.
At step st6, a brightness of a backlight unit is controlled by the modulation factor s, which is used for generating the conversion image data Dc. Here, the brightness of the backlight unit may be controlled to decrease by 1/s times or more than 1/s times.
According to the method of driving an LCD device of the first embodiment of the related art, the power consumption of the LCD device decreases by about 20 percent without lowering the image quality. Thus, driving time of the LCD device in small models can be further extended.
FIG. 2 is a flow chart of illustrating a method of driving an LCD device according to a second embodiment of the related art. FIG. 3 is a view of illustrating a histogram for source image data in a method of driving an LCD device according to the second embodiment of the related art, and FIG. 4 is a view of illustrating a histogram for conversion image data in a method of driving an LCD device according to the second embodiment of the related art.
At step st11, source image data Ds corresponding to one frame, each of which has one of m gray level values (m is a natural number), are inputted as n bit digital data (n is a natural number) from exterior circuits such as a timing controller. Here, m is 2n, and the inputted source image data Ds are R, G, and B color image data that are supplied to a liquid crystal panel to produce an image. For example, the source image data Ds may be 8 bit digital image data for 256 gray levels. That is, n may be 8, and m may be 256.
Next, at step st12, referring to FIG. 3, T source image data (T is a natural number), which have top some gray level values from the largest gray level value, are defined as error data Er. The number of the error data Er, that is, T can be changed according to a designer.
At step st13, a modulation factor s is calculated by a maximum image data Dmax having the largest gray level value from the source image data Ds excluding the error data Er, and conversion image data Dc are generated through the above-mentioned steps st3 and st4. A histogram of the conversion image data Dc is shown in FIG. 4.
At step st14, the conversion image data Dc are inputted into the liquid crystal panel to display an image.
At step st15, a brightness of a backlight unit is controlled by the modulation factor s.
In the second embodiment of the related art, since the inputted data are data-modulated after the error data Er are determined from the inputted data, the modulation factor is larger than that of the first embodiment of the related art. In proportion to this, the power consumption of the backlight unit is further reduced as compared with the first embodiment of the related art.
By the way, the error data Er are data-modulated such that the data-modulated error data have the maximum gray level value, that is, the mth gray level value due to gray saturation properties.
If the error data are densely disposed in a certain region of the liquid crystal panel, the region may be displayed relatively brightly and may be easily recognized by a viewer. This may cause degradation of the image quality.